I was always taught that a website is no different to a glossy magazine - say a Conde Nast publication - albeit interactive. Layout, colours, etc. - the thinking behind these isn't any different to the print world.
Ever read a glossy magazine that says "printed by: XXX" on the bottom of each page? The publisher would be livid. And the audience would think "cheap pineapples!" Would you send wedding invitations out and allow the printers to say "Design & printed by ZZZ"? Why is it that the cheap business cards by Vista (with their ad on the back) are thought of as cheap compared to the Premium cards?
I feel if your site is devoid of sponsorship\ads - then it should not have a "designed by XXX" on the footer. If you feel there is value in the reciprocal link then you could just as easily put it on a separate page called Links, along with whatever else is you think is good\useful. Even if your site is showing advertising - I'd still move the designer to a Links page.
In the print world - and whilst the electronic world does have some peculiarities (I'd probably say enhancements in terms of functionality) - credits, etc. are kept to their own page. Not on the bottom of each page.
Sorry - not dissing anyone, just my 2c worth.
Dibs